This study aimed to evaluate the physiological behavior of faveleira (Cnidoscolus quercifolius Pohl) plants grown in the field, in Caatinga, during wet and dry seasons. Adult plants were selected for evaluation in March and April (wet season) and May and June (dry season), during 2016. We evaluated the soil water content, water potential (Ψw), osmotic potential (Ψπ), relative water content (RWC), stomatal conductance (gs), transpiration rate (E), photosynthetic rate (A), intercellular CO2 concentration (Ci), instantaneous water use efficiency (A/E) and carboxylation efficiency (A/Ci). The reduction in water availability in the soil promoted a marked decrease in soil water potential, which was more affected than the relative water content. The opening of the stomata was affected by the decrease in soil moisture content, reducing the stomatal conductance, transpiration rate, photosynthesis rate, instantaneous water use efficiency and carboxylation efficiency. The photosynthesis was more affected than transpiration by the reduction in soil moisture content.

This study aimed to investigate the gas exchange, growth and biomass production of Cnidoscolus quecifolius fertilized with potassium and submited to different water conditions. The experiment was conducted in a completely randomized design, with 4 replications and two plants per experimental unit, with treatments arranged in factorial scheme 3 × 4, corresponding to three levels of potassium (0 (control), 97.5 and 195 mg dm-3 K) and four levels of water (100% (control), 75%, 50% and 25% of pot capacity). Growth (height, shoot diameter, leaf area, and dry mass) and physiogical parameters (water potencial (Ψw), stomatal conductance (gs), transpiration rate (E), net photosynthesis (A), CO2 intercelular concentration (Ci), carboxylation efficiency (A/Ci), and intrinsic water use efficiency (A/E). Increase in potassium promoted rise in Ψw, gs, E, and A. However, it not influenced the growth parameters, except roots dry mass. Reduction in water levels reduced Ψw, gs, E and A, growth and dry matter production of plants. It is recommended that the substrate moisture level of 75% of the pot capacity in the early growth stages of faveleira seedlings.

A craibeira (Tabebuia aurea (Manso) Benth. & Hook. F ex S. Moore), pertencente à família Bignoniaceae é uma espécie que ocorre entre os biomas Caatinga e Cerrado frequentemente encontrada em margens de rios e lagos compondo as matas ciliares onde há uma maior quantidade de água no solo. Em virtude da falta de conhecimentos a respeito de aspectos relacionados à fase de viveiro dessa espécie, conduziu-se este experimento com o objetivo de avaliar o crescimento inicial e a produção de matéria seca de plantas de craibeira em função de doses de potássio e de níveis de água. O experimento foi conduzido em garrafas plásticas tipo Pet, contendo 2,5 kg de terra, distribuído em delineamento inteiramente casualizado, arranjados em esquema fatorial 3x4, sendo 3 doses de potássio (0 (controle), 97,5  e 195  mg dm-3 K) e 4 níveis de água (100%, 80%, 60% e 40% da capacidade de vaso (CV)). A redução nos níveis de água promoveu diminuição no crescimento e na produção de matéria seca das plantas. O regime hídrico ideal para o crescimento das mudas foi 100% da capacidade de vaso. A adubação potássica não exerceu influência na altura, mas favoreceu a produção de matéria seca nas raízes e a matéria seca total das plantas.